It has been hitherto known that N-substituted-2-amino-4-(substituted-oxymethylphosphinyl)-2-butenoic acid ester is a synthesis-intermediate of L-AMPB having herbicidal activity (Japanese Patent Kokai Publication No. S62-226993A (1987) (Patent Document 1) and J. Org. Chem., 56, 1991, 1783-1788(Non Patent Document 1)).
Up to date, a process for synthesizing by condensing 2-oxo-4-(hydroxymethylphosphinyl)-butenoic acid with acetamide and a process for synthesizing by condensing a derivative of phosphinylacetaldehyde with isocyanoacetate have been reported as a processes for producing N-substituted-2-amino-4-(substituted-oxymethylphosphinyl)-2-butenoic acid ester. (Patent Document 1).
The process for synthesizing dehydroamino acid by a reaction of the Horner-Emmons type with a derivative of phosphorylglycine and aldehyde has been known (Synthesis, 1992, 487(Non Patent Document 2)).    Patent Document 1: Japanese Patent Kokai Publication No. S62-226993A (1987)    Non Patent Document 1: J. Org. Chem., 56, 1991, 1783-1788    Non Patent Document 2: Synthesis, 1992, 487